Date: Mon, 13 Jul 2015 14:01:55 -0400
From: Mike Snitzer <snitzer@redhat.com>
To: Milan Broz <mbroz@redhat.com>
Cc: Joseph Salisbury <joseph.salisbury@canonical.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-kernel@vger.kernel.org, JBottomley@Parallels.com,
        Kernel Team <kernel-team@lists.ubuntu.com>, jgarzik@redhat.com
Subject: Re: dm-crypt: never use write same (was Re: [v3.7 Regression] [SCSI]
 sd: Implement support for WRITE SAME)
Message-ID: <20150713180155.GD30898@redhat.com>
References: <50CB8C74.3090102@canonical.com>
 <yq11uesdzya.fsf@sermon.lab.mkp.net>
 <50D0C971.1000907@canonical.com>
 <yq1bodq7zdv.fsf@sermon.lab.mkp.net>
 <20121219195801.GA14456@redhat.com>
 <50D22766.9090107@redhat.com>
 <50D22C7F.2020201@redhat.com>
 <50D23DA3.9060104@canonical.com>
 <55A3E843.9080209@canonical.com>
 <55A3EEF3.9080106@redhat.com>
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On Mon, Jul 13 2015 at  1:01pm -0400,
Milan Broz <mbroz@redhat.com> wrote:

> (sorry, resending again, not sure if it was sent correctly)
> 
> On 07/13/2015 06:33 PM, Joseph Salisbury wrote:
> > Hi Milan,
> > 
> > The Ubuntu kernel has been carrying this patch since the discussion[0]
> > we were having about the bug.  I don't see that patch was ever included
> > in mainline.  Do you happen to know if this patch is still needed or was
> > the bug we were seeing fixed in some other way?
> 
> I think it was superseded by later Mike's approach to reverse the logic
> - disable write same for all targets and require to explicitly allow it.
> 
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/md/dm-table.c?id=c1a94672a830e01d58c7c7e8de530c3f136d6ff2
> (+later patches)
> 
> So I think we do no need this patch upstream anymore.
> 
> Mike, am I right here?

Yeah, a DM target needs to opt-in by setting ti->num_write_same_bios
(only linear, stripe and mpath do at this time).
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